Grinding machine



March 1 M. I. MATHEWSON arm. 5,558

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' GRINDING MACHINE Original Filed Nov. 14; 1935 9 sheets-sheet:

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GRINDING MACHINE Original Filed Nov. 14, 1935 9 Shuts-Sheet 3 (IttornegsMarch 1941- M. l. MATHEWSON ETAL 2,235,553\

GRINDING IACHINE 9 Shasta-Sheet 4 ZSnventors W 1 mmx l LA Original FiledNov. 14, 1935 S am M/ v a mm, Q \Q m n v w Nam m mum m 3m NM. Q 1 u 8 \I.il: 7 8% w mam Q Q March 18, 1941- M. 1. MATHEWSON arm.

GRINDING MACHINE Original Filed NOV. 14, 1935 9 Sheets-Sheet 5 .JHM a3.5a? NNN mm Ohm. T QN Q SE @LE m QR March 1941- M. I. MATHEWSON ETAL 35558 GRINDING MACHINE 9 Sheets-Sheet 6 Original; Filed Nov. 14, 1935March 1941. M. l. MATHEWsoN ETAL' 35.5

GRINDING MACHINE Original Filed Nov. '14, 1935 9 Sheets-Sheet 7 w m n eD n 3 MM: 18, 1941. M. I. MATHEWSON ml. 2235558 GRINDING IACHINEOriginal Filed Nov. 14, 1935 9 Sheets-Sheet 8 3 E5 3% Emmi O 226. mot.EEM

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M. l. MATHEWSON ETAL GRINDING MACHINE 9 Sheets-Sheet 9 Fig. 21

STARTER Original Filed Nov. 14, 1935 LINE GRIND 3 I' '34 g 15 4 3 35TfflJE 35 5K 4 srmubai' ALONE LEFT siownowu PLUNGE uni 3 Tkz bm$ =g 1ISnventors Gttornegs 271M ywzm Patented Mar. 18, 1941 warren STATESPATENT OFFICE GRINDING MACHINE Rhode Island Original applicationNovcmhcr 14, 1935, Serial No. 49,772. Divided and this applicationOctober 4,

1937, Eeriai No. 167,190

34 @laims.

The present invention relates to improvements in grinding machines, andmore particularly to operating and control devices for impartingtranslatory movements to a reclprocable work 5 table of such a machine.

It is a principal object of the invention to provide novel operating andcontrol devices for driving the work table which will be readilyadjustable to control the operation of the table for a 10 wide varietyof operating conditions which may include both power and manualoperation.

It is a further object of the invention to provide a novel slow-downmechanism for the table which is rendered operative under certain oper-15 ating conditions to insure an accurate and dependable control oftable reversal. It is another object of the invention to provide in atable controlling and driving mechanism of this general description, anovel and im- 10 proved dwell mechanism which is operative to secure apredetermined amount of dwell at each reversal in the direction of tabletravel..

it is a further object of the invention to provide electrical operatingand controlling devices iii for the work table which may well form anintegral part of an electrical operating system for the machine, andwhich are well adapted to insure at all times a dependable and accurateoperaticn of the table over a wide range of operating 30 conditions, ashereinafter more particularly set forth.

The invention is herein disclosed in a preferred te m in a grindingmachine of the general type lch comprises a longitudinally movable worktable having supported thereon a rotatable work holder in the form ofthe usual headstock and tailstock. a power driven grinding wheelspindle, and a wheel spindle carriage which is supported on cross waysfor movement toward and away from the work. The several cooperatingmechanisms of the machine are electrically driven and controlled bymeans of a number of electric motors, as fully set forth in applicant'scopending application Serial No. 49,772, filed November 14, 1935, nowPatent No. 2,165,898 of which the present application is a division.

The work table of the present machine is driven by means of a directcurrent motor which is controlled by a field rheostat to permit a widelatitude in the rate of drive. The table motor is reversible to reversethe direction of drive, and is connected to the table through apower-hand clutch and a fast'slow clutch in series therewith. so thatalternate fast and slow driving rates are available for either power ormanual opera- 'tion oi the table.

In accordance with the invention, manually operable controls for thetable are provided which include separate fast-slow'selector controlsfor 5 determining the position of the fast-slow clutch under alternativeconditions of manual and power operation, and a power-manual controlelement which is arranged to shift the position of the power-manualclutch and at the same time to render one or the other of said selectorcontrols operative to determine the rate of table travel. In order topermit a quick adjustment of the table for the desired rate of poweroperation, a control element for the field rheostat above mentioned, isprovided, having a slow speed range and a high speed range indicatorscale which provide for a direct adjustment of the motor speed for thedesired rate of table travel with the fast-slow clutch in each of itshigh speed and low speed positions.

Another feature of the invention consists in the provision of a novelarrangement of the manual controls for starting and stopping the table,and for stopping the table at the end of its travel in either direction.

Reciprocation of the table is controlled by means of reversing dogs onthe table which cooperate with a reversing lever to reverse the tablemotor. In accordance with one feature of the present invention, a novelarrangement of reversing switches and operating connections thereforfrom the reversing lever is provided which is particularly well adaptedto limit the overrun of the table upon reversal within ascertainablelimits. The connections provided comprise a right and left limit orreversing switch, and right and left slow-down switches which arecontrolled by means of a cam actuated by the movement of the reversinglever from one oper- 4O ating position to the other. With thearrangement described, each of the slow-down and reversing switches isrendered operative when the reversing lever reaches a predeterminedangular position, so that the table is electrically slowed and thenstopped in a position which corresponds to the angular position reachedby the reversing lever, and may be determined within narrow limitsthrough the operation of the electrical braking connections hereinafterdescribed.

In order to provide a positive limit for movement of the table in eachdirection where it may be desired to move the grinding wheel beyond thenormal stop position against or closely adjacent a shoulder on the work,two positive stops 55 table only when the fast-slow clutch is in itshigh speed position.

Further in accordance with the presentinvention, the electrical devicesfor controlling the-operation of the table are constructed and arrangeda to provide a dwell in table operation at reversal.

said devices in the preferred form of applicants construction beingadjustable to vary or, if so desired, t'o entirely eliminatethe tabledwell at each end of its travel in each direction.

The several features of the present invention consist also in thedevices, combinations and arrangement of parts hereinafter described andclaimed, which together with the advantages to be obtained thereby willbe readily understood by one skilled in the art from the followingdescription taken in connection with the accompanying drawings, in whichFig. l is a view in front elevation of a, grinding machine embodying theseveral features of the invention; Fig. 2 is an enlarged view in frontelevation illustrating particularly the table drive, overlying portionsof the machine having been broken away to show underlying parts; Fig. 3is a sectional view taken substantially on the line 3-3 of Fig. 2,being. a somewhat modified plan view of the table driving'connections;Fig. 4 is a sectional view taken on the line 3- of Fig. 2, toillustrateparticularly the power-manual clutch and solenoid control therefor; Fig.5 is a sectional view taken on the line 55 of Fig. 2, illustratingparticularly the table slow-fast clutch and solenoid control therefor;

Fig. 6 is an enlarged detail view in front elevation with certainoverlying parts broken away to illustrate particularly the reversinglever and reversing switch mechanism therefor, the parts beingillustrated in a hypothetical halfway position; Fig. 7 is a sectionalview taken on the line 'I--'l of Fig. 6; Fig. 8 is an enlarged view infront elean enlarged scale the table end stop switch; Fig.

12 is a detail sectional view looking from below taken on the lineI2--i2 of Fig. 8, to illustrate on an enlarged scale the table stoppingswitch; Fig. 13 is a sectional view looking from below taken on the line13-!3 of Fig. 8, to illustrate particularly the table stopping switch;Fig. 14 is an enlarged view in front elevation of the right hand half ofthe control panel for the machine, a portion of the panel being brokenaway to show particularly the table slow-down and limit reversingswitches; Figs. 15 to 18 inclusive, are similar views of the tableswitch connections illustrated in Fig. 14, and with Fig. 14 illustratein five successive steps the positions taken by said switch connectionsduring the movement of the reversing lever to reverse the direction oftable drive from right to left; Figs. 19 and 20 constitutea wiringdiagram of the electrical connections for the'machine, Fig. 19illustrating particularly the electrical connections on the machinecontrol aeeae s panel, and Fig. 20 illustrating subsidiary switchconnections controlled thereby for controlling the operation of theseveral operating units of the machine; and Figs. 21 and 22 constitutingan explanatory diagram of the electrical connections, Fig. 21 beinganexplanatory diagram of the electrical connections for certainof theoperating units, and Fig. 22 being an explanatory diagram moreparticularly of the direct current control circuit of the machine.

The machine illustrated in the drawings as embodying in a preferred formthe several features of the present invention, comprises a base 962, awork supporting table te l which is arranged to slide in ways itit .onthe base, a head stock bracket i8 8 adjustably secured on the table, afoot stock Mil also carried on the table, and a grinding wheel carriageM2 which is supported on cross ways (not shown) on the base.

The work supporting table is driven from a variable speed reversibledirect current motor 832 as best shown in Figs. 2 and 3 of the drawings,through driving connections which comprise a pinion 53% mounted on thearmature shaft tilt of the motor to mesh with a gear list secured to arotatable shaft 5:30. The gear i238 meshes also with a sleeve drivinggear M2 which is externallysupported in a bearing M6, and has formed atthe inner or forward end thereof a clutch face Me for engagement with acooperating clutch surface' 152 carried on the shiftable element ofthepower-manual clutch. The shiftable clutch element referred to,- takesthe form of ,a shaft I52 supported for axial and rotational movements atone end within the sleeve hub of the gear M2 and at its other end in abearing E53 on the machine frame. Rigidly secured to the shaft I52 is ahigh speed driving gear lEG which has formed thereon the clutch face.B50, and a slow speed driving gear i56.

Iii-order to provide for the manual operation of the table, there isformed on the end of the shaft I52 a clutch face ififi which is arrangedto engage with a clutch member I62 formed on the adjacent end of a handwheel shaft wt in axial alignment therewith. The shaft Hi l is supportedin bearings 866 in the machine frame, and carries at its outer end atable traversing hand wheel its. At its inner end the shaft i6 3 isprovided with an axially extending pin iiil which extends into an axialbore in the abutting end of the shaft 952 to maintain the two shafts inaxial alignment. v

The gears we and mesh respectively with gears H6 and H6 which areloosely mounted to turn on a rotatable shaft H8, and form respectivelythe fast and slow driving elements of a fast-slow clutch unit. A drivenclutch element is splined to the shaft 1118 between the driving gearslid and lit, and is arranged for axial movement in either direction toengage alternatively with. cooperating clutch members formed on theadjacent faces of the driving gears. A pinion its also secured to theshaft H8 meshes with a gear ltd secured to a drive shaft I86 which alsocarries the table driving pinion 1188, which in turn meshes with a racki913 formed on the underside of the table. With this construction andarrangement of parts, it will readily be seen that the table may beconnected alternatively for power or manual operation ,by an axialshifting of the power-manual clutch shaft I52 including the gears I54and E56. The table may then be driven selectively at a high or low rateof speed either by power or manually in accord- 75 ance with theposition of the fast-slow clutch I80 as desired.

The position of the power-manual clutch for the table is controlled froman electrical control system for the machine hereinafter to bedescribed, by means of a solenoid 200 and a clutch actuating lever 202(see Figs. 2 and 4) which is mounted to turn on a pivot shaft 204, andis connected at one end to the solenoid armature 206, and at its otherend to the axially movable clutch shaft I52. Th lever 202 is connectedat its upper end to the clutch by means of two bearing blocks 20? whichare pivotally supported on the forked upper end of the lever to engagein a peripheral groove formed in the sleeve hub 208 of the gear 454rigidly secured to the clutch shaft l52. At its lower end the clutchlever 202 is connected to the solenoid armature 225 by means of a linkare which is pivctally connected at one end to the armature, and isprovided with a reduced portion which extends through a bore formed in across pin 252 supported in the forked lower end of the clutch lever. Acompression spring EM coiled about the reduced portion of the link 256between a collar 2&6 and the cross pin 2S2, tends to maintain the clutchlever 2&2 yieldingly against an abutting shoulder on the link us. Themovement of the clutch lever 202 in either direction is limited byengagement with adjustable stop pins H8 and 22d screw-threaded into themachine casing, and arranged for contact with opposite sides of thelever. Two tension springs 222 connected at one end to the clutch lever262, and at their other ends to a pin 224 on the frame, tend normally toswing the clutch lever in a clockwise direction as shown in Fig. 4, toshift the clutch in a direction to disengage the power clutch member M8and to engage the hand wheel clutch $62. With this construction andarrangement of the parts, the energizing of the solenoid its will causethe clutch lever to be shifted in a counterclockwise direction againstthe pressure of the spring 222 to disengage the hand wheel clutchelement I62 and to engage the power clutch member M8 for power operationof the table. The yielding connection provided by the spring 2M betweenthe solenoid armature 286 and the clutch lever 222, permits the armature265 to be moved immediately to power position upon energizing thesolenoid, and thus to avoid possible injury thereto, although the actualshifting of the clutch may be delayed while the clutch teeth are broughtinto alignment.

The position of the slow-fast. clutch member |80is controlled from theelectrical control system for the machine, by means'of a solenoid 226and a clutch actuating lever 228 (see Figs. 2 and 5) which is pivotallyhung from a pivot pin 23d. The clutch lever 226'; takes the form of aframe on which are supported bearing blocks 232 ar ranged for engagementin a peripheral groove 23% formed in the clutch member I80. [it itslower end. the clutch lever 225 is connected to the armature or" thesolenoid 226 by means of a link 23% having a reduced portion whichextends through a bore formed in a cross pin are supported in the forkedlower end of the clutch lever. A yielding connection is provided betweenthe clutch lever 228 and armature 236 by means of a compression spring24! which is coiled about the reduced portion of the link 238 between acollar 242 on the end thereof, and the cross pin 240, so that the lever228 and cross pin 242 are held yieldingly against an abutting shoulderformed on the link 238. The fast-slow clutch in is normally held in itsfast position by means of two parallel tension springs 244 which areconnected at one end toa cross pin 248 on the lever 228, and at theirother ends to a pin 2 on the machine frame. The movement of the clutchlever 228 in either direction is limited by means of adjustable stoppins 250 and 252 screw threaded into the machine frame.

The reciprocation of the work table is controlled bymeans of table dogsand a reversing lever which operate through switch connectionshereinafter to be described, to stop and thereafter to reverse thedirection of rotation of the table motor I32. Two reversing dogs 260 and262 are provided as best shown in Figs; 1, 6 and '7, adjustably mountedin a T-shaped slot 26d, and arranged for engagement with a reversinglever 2% supported on a rock shaft 268 carried in bearings 2Y0 on themachine frame. There are also provided on the machine frame at each sideof the reversing lever, two stop lugs 212 and 2M to positively limit theswinging movement of the lever in either direction under the influenceof the reversing dogs, so that a positive stop is provided for thetravel of the table in either direction. The reversing lever 2 56 isbifurcated to fit over a flattened portion 216 formed on the rock shaft268, and is pivotally connected thereto by means of a cross pin 218, sothat the lever may be swung forwardly out of the path of the re versingdogs, to permit manual operation of the lever independently of the dogs.Secured to the rock shaft 268 is a downwardly extending hookshaped leverarm 28!! which has formed thereon a gear segment 282 arranged forengagement with a pinion 284 secured to a control shaft 286 which issupported in bearings on the machine frame in parallel relation to therock shaft 288.

With the connections above described, the movement of the reversinglever 266 from one operating position to the other, will cause acorresponding rotational movement to be imparted to the control shaft286 in an opposite direction by an amount which will depend exactly uponthe amplitude of movement of the control lever 265.

The oscillatory movements of the control shaft 285 are utilized tooperate a table slowdown and reversing switch to reverse the directionof drive 14 to 18 inclusive, and 20) comprise a right slowdown switchcontact 5556 and a left slowdown switch contact 5651 which operate toslow the motor and table driven thereby to a predetermined slow rate,and a right limit switch contact 3-63, and a left limit switch contact3-65, which operate thereafter to reverse the motor and direction oftable movement. The switch actuating connections comprise a cam 296 on acam shaft 287 which is mounted in axial alignment with the control shaft236 and is keyed to turn therewith. The shaft 28? is supported adjacentone end thereof in a stationary bearing in the machine frame, and at itsother end is provided with an axially extending pin 288 which extendsinto an axial bore in the end of the control shaft 288. A pin 289carried on an enlarged head on the shaft 281, engages with acorresponding aperture formed in the face of the gear 281, so that thecam shaft 281 is keyed to rotate therewith. Two identical switchactuating levers 292 and 29d, pivoted respectively at 29% and 2% on themachine frame, are provided at their free ends with cam rolls arrangedfor engagement with the cam, and lugs 3B and 382 which are yieldinglyengaged by two downwardly pressed switch plungers 36 i and 365 foractuating the switch connections for reversing the direction of drive ofthe table motor. Two tension springs 39B and did connected respectivelyto the switch levers 292 and 29d tend normally to move the leversdownwardly into engagement with the switch cam 2%." Stop pins did andBit serve to limit the downward movement of the levers. The switchplunger 3M carries two switch contactors Bid and M8 which areconstructed and arranged so that when the plunger Std occupies anintermediate position as the switch lever 292 rides on the intermediatelevel of the switch cam 29, both are closed. The movement of plungerSilt to its high position under the influence of the cam 2% causes thecontactor 3th to move away from and open the switch contact 3--t35, themovement of the plunger 3% to its low position conversely causing thecontactor 396 to move away from and open the switch contact 55-55. Theswitch plunger is similarly provided with two contactors 52d and 322which are similarly controlled to close both contactors for anintermediate position of the switch plunger 386,:and to openalternatively the left slow-down contact t-5'i or right limit switchcontact 3- -63 as the plunger is moved to its low or high position' Theoperation of the reversing lever 26% and reversing switch connectionscontrolled thereby, will be readily understood from an inspection ofFigs. 14 to 18 inclusive, which illustrateiive successive positions oithe switch connections taken as the reversing lever is shifted toreverse the direction of table travel from right to left. As shown inFig. 14, the reversing lever is in its extreme position to the leftprior to the engagement of the dog Ztilthrewdth. For this position ofthe reversing lever 256, the cam 299 has been rotated in a clockwisedirection so that the plunger 3% is fully raised under the influence ofthe high portion of the cam, and the plunger 306 is fully depressedunder the influence of the low portion of the cam 29%. For this positionof the parts, the right slow-down switchcon tact 5555 and the rightlimit switch contact I i-63 are closed. The movement of th reversinglever 2% upon engagement of the table dog 2% therewith,

now causes the cam 2% to rotate in a counterclockwise direction. Asshown in. Fig. 15, the switch lever 292 is moved onto the intermediatelevel of the cam 29B, causing the left limit switch 365 to be closed,but without otherwise altering the operating conditions electrically. Asshown in Fig. 16, the switch plunger 34% is now moved to its retractedposition as the switch lever rides from the intermediate to the lowportion of the cam 290, causing the contact MB to be disengaged from theright slow-down contact Sid-56 to shift the motor to slow speed. Thecontinued rotation of the cam 2% as the reversing lever 2'66 swingsstill further towards its limiting position to the might, now causes theswitch lever 285 to r-ideonto the intermediate portion of the cam 290 asshown in Fig. 17, to close the left limit switch contacts 56-57, andsubsequently, as

the switch lever 296 rides onto the high portion of the cam 290, todisengage the switch contactor 322 from the right limit switch contact3-S3, causing the motor to be reversed. In order to shift the tabletravel from the left to right,

aaeacce the operation is exactly the reverse. The opening of the leftslow-down switch contact dfi-S'i will cause the motor to be slowed to apredetermined speed, and the subsequent opening of the left Limit switchcontact 3-65 will again reverse the direction of rotation of the tablemotor. In order to permit the braking torque of the motor to bring thetable smoothly to a stop upon reversal, and also to permit a certainamount of variation in the overrun oi the table in either direction, thecam 29 and connections to the reversing lever 2% are so arranged as topermit a certain amount of overthrow of these parts after the motor hasbeen reversed. The reversing lever 2% does not normally en age the stopabutments are and 215 during reversal. However, it is frequentlydesirable to stop the power operation of the machine at the end or itstravel in either direction, and thereafter by manual operation thereofto bring the grinding wheel up to or briefly into contact with anabutting shoulder of the work. The engagement of the reversing lever.against the shoulder. The operation of the subsidiary electricalconnections controlled by the opening of the switch slow-down andreversing contacts above described, to effect the corresponding changesin the operating conditions of the machine, will be further described inconnection with the electrical diagram (Figs. 19 to 22 inclusive).

The machine disclosed in the drawings, is provided, with an electricalcontrol system having a number of novel features of construction andoperation well adapted to insure an accurate and versatile control ofthe work supporting table for operation under a wide variety ofoperating conditions. These controls include power and-manual fast-slowselector switches operative alternatively to control the rate of tabletravel depending upon the position of the power-manual clutch, a noveland improved starting, stopping and end stop control for the table,together with electrical connections arranged under certain operatingconditions to provide a table slow-down and a table dwell upon reversal.

The electrical driving and operating controls for the table form a partof the electrical system for the entire machine. For clarity ofillustration, the electrical diagram of the operating con- -nections forthe machine, is disclosed in its enalternating current motors includingthe main grinding wheel spindle motor 313, the coolant pump motor 534,the lubricant pump motor 668, the cross feed rapid movement motor 510,and a generator motor ltd which is in turn directly connected to drive aheadstock motor generator TM and a table motor generator 832. The headstock generator is a constant potential self-excited generator whichsupplies the necessary power for running the head-stock motor H8, andalso supplies current to the direct current control circuit hereinafterto be described. and to the fields of all of the direct current motorsand generators above mentioned.

The several manually operable controls for the machine are mounted on acontrol panel 133 which is mounted on the front side of the machinebeneath the table. These controls include a machine Start button 734 anda Stop button 735 which operate to control the starting and stopping ofthe main spindle driving motor 6'13, the generator motor 130, the oilpump motor 688,

and the coolant pump motor 834. The pushing of the Start button 134, asbest shown in the electrical diagram illustrated in Figs. 19 and 20, andin the explanatory diagram Fig. 21, operates to close the contacts 'l583to energize the starting switch solenoid 136, which in turn operates toclose the main line contacts 'I5-3l, id-98 and Tl35, and also a holdingswitch contact 75 -84. The pressing of Stop button "135 operates to openthe contact 82-43 to deenergize the mainswitch solenoid 136, and thus tostop the machine.

Ihe starting of the generator motor 130 and headstock generator l3!operates immediately to supply current to the entire direct currentcontrol circuit which, as best shown in the explanatory diagram Fig. 22,comprises a supply line i, 3 and a return line 2, 4. The headstock motorarmature designated at 131 and the headstock motor shunt field 738 areconnected across the supply and return wires l, 2. In order to permitvariations in the motor speed, a headstock field rheostat HR is providedin series with the shunt field 738. This rheostat is controlled by meansof a knob 239 on the left side of the panel 133 to determine the drivingrate of the headstock motor.

In. accordance with the present invention, there is provided on thecontrol panel 733, a table control knob 159 which is rotatable in aclockwise direction to start the table motor and table, and-rotatable inan opposite direction to stop the table motor and disconnect the powerdrive. The table knob may also be pressed downwardly by the operator tocausethe table motor to be stopped and the table drive to bedisconnected when the table reaches the end of its travel in thedirection in which it is moving at the time of pressing the knob. Thetable knob 159 is rigidly secured, as best shown in Fig. 8, to the upperend of a rotatable and axially movable switch control rod "I60 which isheld normally in ,a raised rest position by means of a compressionspring 'lSi which is coiled about the control rod 780, and, is seated atone end within a recess formed within the table knob 159, and at itsother end within a recess formed in the panel casing 133. There arerigidly secured to the control rod 750, a table starting switchactuating arm H54 (see Figs. 8 and 13) and a stop switch control arm766. The table starting switch comprises a plunger 168 which carries twoswitch arms m and I72 and is normally held in a rest position to theleft in engagement with the lever arm 784, as shown in Fig. 8. by meansof a compression spring 714, in which position the switch arm H engagesthe contacts 50--5|. The table stop switch similarly comprises a switchplunger "8 having mounted thereon switch arms 780 and 182 and isprovided at one end with an enlarged head which engages with a forkedportion of the switch lever arm 166. A compression spring 184 tendsnormally to move the plunger to the right, as shown in Fig. 8, so thatthe switch arm 182 is normally positioned to close the contacts 54-53.The table end stop switch comprises a switch plunger 186 which carriesswitch arms I88 and 190 and is arranged to engage against one arm of asmall bell-crank lever 392, the other arm of which engages the lower endof the table switch control rod 160. A compression spring 794 tendsnormally to maintain the switch plunger 186 to the left, as illustratedin Fig. 8, with the switch arm 790 out of engagement wit-h the contacts5i-52.

The operation of the table motor is controlled from the table knob 759and the starting and stopping switches above described by means of anumber of secondary switch connections which include table dwell relays'IRi and 5H2, generator field reversing contactors L and R,

o a hand wheel solenoid contactor HWS; under voltage contactor UV, tableline and dynamic brake c0ntactor LEE; counter electromotive forces relayCEMF; table slow speed contactor SS and a table slow-down contactor S.The table dwell relays TR! and TR2 are carried one. panel 796illustrated at the top of the wiring diagram Figure 19, the tableslow-down contactor S is mounted on the panel E58, and the remaining oithe above-mentioned switches are located on a panel 188, as best shownin Fig. 19.

For starting the table if it be assumed that the several controls of themachine, as fully described in the parent application above referred to,are set for Grind position, Knob control, Long dwell, and Run position,the turning of the table knob 159 in a clockwise direction causes thelever arm lii l to engage with and move the switch plunger T53 to theright to.close the switch contacts bib-55 and simultaneously to open thecontacts ESL-5i, thus energizing coil UV. Contact UV i375a3 closes,energizing LE5 and either L or E coil, depending upon the position ofthe reversing lever. It will be hereinafter assumed that coil R isenergized. Contact UV 22-23 closes, decreasing the table dynamic brakingresistance, and contact UV 38-39 closes, energizlng coil I-IWS which inturn energizes the solenoid 2% to disconnect the hand wheel from thetable and engage the table drive to the table motor i32. Contact LEi11-89 closes, starting the table motor and energizing coil CEMF, andcontact LEE 2il--2i opens, disconnecting the dynamic braking resistorR5.

TR2 59-?!) opens, and contact TR 3-59 closes,

Contact TRi 18-4 opens.

energizing coil mi. The contacts TR2 69-48 and THE id-4 must both closebefore a table reversal can take place. Contact I-IWS ii-72 opens,disconnecting the hand wheel fast-slow selector switch, and contact HWS13-72 closes, placing the power fastslow selector switch in series withcoll SS. Contact SS i2-i3 closes, giving the table motor a speed, asdetermined by the table field rheostat 791. The setting of the rheostat1537 is controlled manually by means of a knob 799 on the panel 133 asbest shown in Figs. 1 and 14.

If it is now desired to stop the table traverse to the right, theoperator may turn the table con Counter EMF 338 closes, contact B -86opens, thus preventing Contact S iii-43 opens placing the total resist=ance of the rheostat in series with the table generator field. ContactLEl ill-l9 opens, disconnecting the table motor, and contact LEl iii-iicloses connecting the dynamic braking resist= ance so as to bring thetable motor to a rapid stop. Contact R tile-to closes, contact R ee-sopens, contact R 3-il opens deenergizing coil TR2, contact R se-sropens, and contacts R l t-45 and R d-lt open, tie-energizing the tablegenerator field. Contact TR? tieid closes, and contact 'iRiZ 3-5Q opens,tie-energizing coil 'IRi and thus causing contact TRi ill- 5 to close.

The coil JED/IF does not tie-energize until the table motor has sloweddown mnsideraloly. This holds the table drive clutch engaged with themotor during the stopping period. Contact CEW 3tt opens, (le -energizingcoil HWS. Contact HWS tit-96 opens, die-energizing the hand wheelsolenoid which engages the hand wheel.

Assuming that the table is travelling to the right and that thereversing lever is shifted by engagement with the table dog 25% toreverse the direction of travel of the table, the move= ment of thereversing lever to the right-as best shown in Figs. 14 to 18 inclusive,first operates to open the right slowdown contact EMQ, as the switchplunger 3% moves to its low position following the movement of the camlever which passes from the intermediate to the low portion of thereversing switch earn 2%. The opening of the switch contact de-energizesthe coil S so that contact S ii-43 opens to throw in the entireresistance of the rheostat ill? to drive the table at a predeterminedlow speed, slowing down the table motor. Subsequently, as the reversinglever nears the limit or" its movement to the right, the right limitcontact opens as the switch plunger 3% of the reversing switch is movedto its highest position by the movement of the cam lever 29% onto thehighest portion of the switch reversing cam so that the coil R isde-energized. Contact R lidll now closes, contact R lit-53 opens,contacts it 'll,l 5 and R 3-45 open de=energizing the table generatorfield, and contact R opens do energizing coil 'IRZ. Coil ml isole-energized by the opening of contact R Contact LEi il-l9 opens,stopping the'talole motor, and con tact LEI 2tl-2l closes, forming adynamic braising circuit which brings the table motor to a rapid stop.The CEMF coil is de=energized as I the motor finally stops and contactSEW 33- 38 length of time which may, for erple, amountto three-quartersof a second after cell TR? is de-energized, it operates to close contactTRE @9-76 and to open contact 2 i l-t9, de-energizing coil "IRi which,after the further delaypreferably adjusted to three-quarters of asecond, operates similarly to close contact 'IRl lE-t. The closing ofcontact TRl re-e energizes coil LEl and L. Contact LEE ll-lfi closes,starting the table motor, and contact LEl Zfi-iii opens, disconnectingthe dynamic braking resistance. Contact L t3-tt opens, making itimpossible to energize coil R, contact L 6M closes holding circuit forcoils LEI and L, contact L 55-55 closes energizing coil S, thuseliminating the slow-down, contacts L d-id and L ii flh close,

energizing the table generator held in an opposite direction from thatin which it was connected during the traverse to the right and contact L3-=6@ closes energizing coil TRE. Contact 5 iii-i3 closes, giving thetable motor speed as controlled by the rheostat in the table generatorfield. Contact TRZ its-it opens, and contact TR? 3-59 closes energizingcoil TBA causing contact TEE it-4 to open.

Assuming that the table is. travelling to the right and that it isdesired to operate the end stop control to cause the table to stop whenit reaches the limit of its travel to the right, the operator pressesdownwardly upon the table knob E59, closing the end stopswitch contact5l-52. Assuming that the controls of the machine are set for Grindposition, Knob control, Long dwell and Run position, the operation ofthe subsidiary switch connections to stop the table travelling to theright, will be as follows: The closing of thecontact tl-52 energizes anend stop contactor coll ES supported on the panel lot which is arrangedto form aholding circuit for itself and to stop the table at the end ofits stroke by holding the circuit open to the reverse contactors L and Rafter the limit switch has been operated. and permits the power -manualclumh to be shifted to hand wheel position. Whencoil ES is energized,the contact ES iii-52 closes, iorrning the holding circuit, contact EStil-till opens, and contactES opens. When the reversing lever is nowmoved to its reversing position by engagement with the table dog coilsml, Pt, ml, Th2, en's/m and S are die-energized as previously describedin connection with the reverssl of the table drive. Gontact GENE opens,ole-energizing coil HWS, which causes the power=rnanual clutch to shiftto hand wheel positlon. Contact TRZ (iii-lid closes, and contact was3-39 opens after its dwell, lie-energizing TEE. Contact Tm Mi l closesafter its dwell. The coils Lil-i and L are not energized because of theopen contact ESBQ-BR leaving the table in its stop position at theextreme right.

in accordance with another feature of the pres ent invention, there isprovided on the control panel W33 a hand wheel fast-slow selector switchmember which is arranged to control the positlon of the fast-slow clutchuse to determine the rate of travel ofv the table during manualoperation or the table hand wheel. This switch, as best shownin theelectrical diagram 28, explanatory electrical diagram Fig. 22, isarranged for the fast position of the switch member 838 to break thecontact 3-76 to tie-energize the table slow speed contactor SS, thuscausing the SS contact Gilto open, de-energizing the slow-fast clutchsolenoid 228, so that the clutch is permitted to move to high speedposition. The alternative slow position of the switch 838 operates toclose the. switch contact S- M, energizing the slow speed contactor S5to close the SS contact @8-95 and energize the solenoid 226 to shift theclutch to slow speed position.

Also provided on the panel 133 is a table power fast-slow control switch840 which is arranged to control the position of the fast-slow clutch I80 during the power operation of the table and has alternative operatingpositionscorresponding to the fast and slow position of the clutch 180The control switch 840 is arranged in fast position to open the switchcontact 3l3 to de-energize the slow speed contactor SS which operates,as above described, to shift the fast-slow clutch iBD to fast position.The movement of the switch mem her 840 to slow position operates toclose contact 3-13 to energize the slow speed contactor SS which, inturn, causes the clutch to be moved to its slow position.

The shifting of the table power fast-slow control switch 848 to slowposition, operates also to disable the electrical connections abovedescribed, for slowing the table prior to reversal. The energizing ofthe slow speed contactor SS causes SS contact 55-41 to close,short-circuiting the right slow-down contactor Eta-56 and the leftslowdown contactor 56-5? to keep the slow-down contactor S energizedduring the continued operation of the table; The shifting of the controlI switch 840 to its fast position, will operate through the opening ofSS contact 5ii5l, to bring the slow-down contactor S under the controlof the slow-down switches. As previously set forth, the de-energizing ofthe slow-down core tactor S through the operation of either the left orright slow-down switch, will operate to open S contact l2|3 to throw inthe entire resistance of the table rheostat 191, thus slowing the tableto a predetermined slow speed prior to reversal.

The control for slowing down the table prior to reversal when operatingat one of the faster rates, has the specific advantage of establishing apredetermined set oi operating conditions prior to reversal. Themomentum of the table is thus greatly reduced, so that the dynamicbraking of the table motoras above described,

- will operate to stop the table with a minimum of overrun, and in aposition which can be determined with considerable accuracy. Duringoperation of the table at one of the lower feed rates, in which thefast-slow clutch N30 is in its slow 'speed position, however, it hasbeen found that the electrical braking of the table is effective to stopthe table without excessive overrun. Under these conditions theelimination of the table slowdown to the extreme slow rate, effects aconsiderable saving in the time required for reversal at each end of thetable travel.

Further in accordance with the present invention, switch connections areprovided for selectively rendering the hand wheel or power fastslowswitch members 838 or 840 operative to control the position of thefast-slow clutch in accordance with Whether the power-manual clutch isset for power or hand wheel operation of the table. To this end switchconnections are provided in each of the hand wheel and power fast- 13-12to render the fast-slow clutch i80 subject to the power selector switch840, and the dcenergizing oi the HW S coil to return the manual powerclutch 150 to hand wheel position similarly operates to open HWS contact13-72 and to close HWS contact 11-12 to render the fast-slow clutch I80subject to the hand wheel fast-slow selector switch.

It will be understood that the invention is not limited to the specificembodiment shown, and that various deviations may be made uherefromwithout departing from the spirit and scope of the appended claims.

What is claimed is:

1. In a grinding machine having a table reciprocable longitudinally foreffecting relative translatory feeding movements of the grinding wheeland work, the combination with the table,

of means for reciprocating the table between limiting positions at auniform rate of travel and for stopping and for starting the table fromsaid positions, said means including an element shift able to bring saidtable to a quick stop, adjustable dogs on said table .to actuate saidshiftable element, and an electrically controlled mechanism to startmovement of the table in the reverse direction after a predeterminedperiod of dwell.

2. In a grinding machine having a table reciprocable longitudinally foreffecting relative translatory'feeding movements of the grinding wheeland work, the combination with the table, of means for reciprocating thetable between limiting positions at a uniform rate, of travel and forstopping and for starting the table from said positions, said meansincluding an element shiftable to bring said table to a quick stop,adjustable dogs on said table to actuate said shiftable element, and anelectrically controlled mechanism including a limit switch actuated bysaid shiftable element, an electrical time delay relay which is set inmotion by said switch, and a solenoid which is energized by said timedelay relay after a predetermined time interval to start the tablemoving in the reverse direction.

3. In a grinding machine having a table reciprocable longitudinally foreffecting relative translatory eeding movements of the grinding wheeland work, the combination with the table, of a reversible electric motorconnected to drive the table, means for controlling the motor toreciprocate the table between limiting positions at a uniform rate oftravel, and for stopping.

and for starting the table from said positions, which comprises ashiftable element and means actuated thereby for braking the motor tobring the table to a quick stop, adjustable dogs on said table toactuate said shiftable element, and electrically controlled mechanismwhich is actuated in timed relation with said shiftable element to startthe motor and table therewith moving in a reverse direction after apredetermined time interval.

4. In a grinding machine having a table reciprocable longitudinally forefi'ecting relative translatory feeding movements of the grinding wheeland Work, the combination with the table, of means for reciprocating thetable between limiting positions at a uniform rate of travel and forstopping and for starting the table from said positions, said meansincluding a reversible electric motor for reciprocating the table, areversing lever, dogs on the table to actuate the lever, and electricalconnections controlled by said lever including a limit switch actuatedby said lever, and means rendered operative by the actuation of said themovement of the reversing lever a predetermined distance from eitheroperating. position to reduce the speed of the motor, and switchconnections rendered operative by further movement of the reversinglever toward the alternate running position toelectrically reverse themotor.

13. In a machine tool, thecombination of a base, a movable support,driving connectionsfor the support including a variable speed reversibleelectric motor, a reversing switch for the motor, electrical connectionsfor actuating said motor at a plurality of predetermined rates,shiftable means in said driving connections for driving the support fromthe motor at fast or slow rates, and control devices for the supportcomprising a reversing lever on the base having alternate runningpositions, cooperating reversing dogs carried on the support to.actuatesaid reversing lever,

, connections rendered operative by the movement of said reversing leverfrom either operating position to the other to electrically reverse themotor,

- and switch connections rendered operative by the adjustment of saidshiftable means to'fast position and controlled by the movement of thereversing lever from either operating position to drive the motor at apredetermined slow rate, and thereafter to electrically reverse themotor at the rate established by said motor variable speed control.

14. In a machine tool, the combination of a base, a movable support,driving connections for the support including a reversible electricmotor, shiftable means in said driving connections for driving thesupport from the motor at a fast or slow rate, and control devices forthe support comprising a reversing lever, and means controlled bysupport movement for reversing the lever, motor reversing limit switchesactuated by the lever, electrical connections for slowing the motorprior to reversal, and means operative upon a shift in said connectionsto drive the support from the motor at the slow rate to disable saidelectrical connections for slowing the motor.

15. In a machine tool, the combination of a base, a reciprocablesupport, a prime mover, and connections therefrom for driving thesupport, a reversing lever on the base having alternative runningpositions, cooperating reversing dogs on the support, connectionsrendered operative by the shifting of the reversing lever by said dogsto I brake to a stop and thereafter to reverse the direction of supportmovement, an end stop control for said braking and reversing connectionsto stop the support in said brake-stop position. manually operable meansfor moving the support, and stops on the base for positivel limiting thecontinued angular movement of the reversing lever spaced to permit alimited manual movement of the support beyond said brake-stop position.I

16. In a machine tool, the combination of a base, a reciprocablesupport, driving connections for the support including a reversibleelectric motor, reversing switch connections for the motor, and controldevices for the support comprising a reversing lever on the base havingalternative running positions, and cooperating reversing dogs on thesupport to actuate the reversing lever, means rendered operative by themovement of the reversing lever in either direction for actuating saidreversing switch connections to electrically brake the support to a stopand to reverse the directionof support movement, an end stop control forsaid reversing switch connections to stop the support in said brake-stopposition, manually operable means for moving the support, and stopsangular movement of the reversing lever spaced to permit a limitedmanual movement of the support beyond said brake-stop position.

17. In a machine tool, the combination of a base, a movable support,driving connections for the support including a reversible electricmotor, and control devices for reversing the support comprising areversing lever on the base having alternative running positions andcooperating reversing dogs on the support to actuate the reversinglever, a switch cam and connections from the reversing lever for movingthe camin opposite directions, said cam having symmetrically ar rangedactuating surfaces, subsidiary connections including left and rightslow-down switches and left and right limit reversing switches, and camfollower connections rendered operative by movement of the lever and camin one direction to actuate the left slow-down switch and thereafter theleft limit reversing switch, and upon movement of the lever and cam in areverse direction to actuate the right slow-down switch and thereafterthe right limit reversing switch.

18. In a machine tool, the combination of a base, a reciprocablesupport, driving connections for the support including a reversibleelectric motor, and control devices for reversing the support comprisinga reversing lever on the base having alternative running positions, andcooperating reversing dogs on the support to actuate the reversinglever, a rotatable switch cam and connections from the reversing leverfor rotating I slow-down switch and aright limit reversing switchcontrolled thereby, a second cam follower engaging the other of saidsurfaces, a right slowdown switch and a left limit reversing switchactuated by the second follower, said cam and follower connections beingarranged during the rotation of the cam with the reversing lever fromone running position to the other first for moving said followers tooperate the slow-down switch correspondin to the direction of tabletravel and thereafter to operate the corresponding limit reversingswitch.

19. In a machine tool, the combination of a base, a reciprocablesupport, driving connections for the support including a reversibleelectric motor, and control devices for reversing the support comprisinga reversing lever on the base having alternative running positions andcooperating reversing dogs on the'support to actuate the reversinglever, a rotatable switch cam and connections from the reversing leverfor rotating the cam in opposite directions, said cam having a centrallow portion and an intermediate and high portion symmetrically arrangedon each side thereof, a cam follower cooperating with each of aid riseportions, a left slow-down switch and a right limit reversing switchconnected upon movement of the follower to the high portion of the camto actuate the limit reversing switch, and upon movement of the followerto the central low portion of the cam to actuate the slow-down switch, asecond cam follower engaging the opposite rise portion of the cam, aright slow-down switch and a left limit reversing switch, andconnections rendered operative by movement of the second follower ontothe high portion of the cam to actuate said left limit reversing switch,and upon movement of the follower to the low portion of the cam toactuate the right slow-down switch.

20. In a grinding machine, the combination with a machine base, areciprocable work table carried thereby, a prime mover and connectionstherefrom for driving the table, means for reversing the tablecomprising a reversing lever on the base and cooperating reversing dogson the table, and control devices for starting and stopping the tablecomprising a manually operable controller, connections renderedoperative by the movement of the controller in one plane to connect saidprime mover to drive the table, or to disconnect the prime mover to stopthe table movement, and connections rendered operative by the movementof the controller in another plane and controlled by the reversing leverto disconnect the prime mover to stop the table at the end of itstravel.

21. In a grinding machine, the combination with a machine base, areciprocable work table carried thereby, a reversible electric motor fordriving the table, a reversing lever mounted adjacent the table,reversing dogs on the table for actuating the lever, reversing switchconnections rendered operative by the movement of the reversing leverfrom one operating position to the other to reverse the motor, amanually operable table starting switch, subsidiary switch connec= tionscontrolled thereby connecting the motor for continued operation underthe control of said reversing lever, a manually operable stop switch afor the motor, a manually operable end stop switch, and switchconnections controlled by said end stop switch to stop the motor whenthe table reaches the end of its travel.

22. In a grinding machine, the combination with a machine base, areciprocable work table,

a reversible electric motor for driving the table,

means controlled from the table for reversing the motor to reverse thedirection of table travel, a manually operable controller, switchconnections rendered operative by the movement of the controller in oneplane to connect the motor for continued operation under the control ofsaid table reversing means or to stop the motor, and end stop switchconnections rendered operative by the movement of the controller inanother plane to stop the motor when the table reaches the end of itstravel.

23. In a grinding machine, the combination ,with a machine base, areciprocable work table, a reversible electric motor for driving thetable, means controlled from the table for reversing the motor toreverse the direction of table travel, a manually rotatable and axiallymovable control knob, spring means tending to maintain the knob in apredetermined angular and axial position, switch connection including aholding circuit rendered operative by the rotation of the knob in onedirection to connect the motor for continued operation under the controlof said table reversing means, a stop switch rendered operative by therotation of said knob in an oppo= site direction to stop the motor, andend stop switchv connections including a holding circuit renderedoperative by an axial movement of the knob and controlled by said tablereversing means to stop the motor when the table reaches the end of itstravel.

24. In a grinding machine, the combination with a machine base, areciprocable work table, driving connections including a reversible variable speed electric motor and a fast-slow clutch for driving the table,means controlled from the table for reversing the motor to reverse thedi= rection of table travel, a manually operable table control includingswitch connections for starting and stopping the motor, a manuallyoperable shifting device for the fast-slow clutch, a manually adjustablemotor speed control including electricalconnections to produce a widerange of motor speeds, and indicator means associated with the motorspeed control having a table slow speed range indicator scale and atable high speed range indicator scale. i

25. In a grinding machine, the combination with a machine base, a workspindle, a reciprocable work table, drivingconnections including areversible variable speed electric motor and a fast-slow clutch fordriving the table, a reversing lever on the base and cooperating dogs onthe table, switch connections controlled from the reversing lever forreversing the motor, connections controlled from the reversing lever'for slowing the motor to a predetermined slow speed prior to reversal,a manually operable table control including switch connections forstarting and stopping the motor, a manually operable shifting device forthe fast-slow switch and connections rendered operative upon shiftingthe clutch to slow position to disconnect said connections for slowingthe motor, a manually adjustable motor speed control includingelectrical connections to produce a wide range of motor speeds, andindicator means associated with the motor speed control having a tableslow speed range indicator scale and a table high speed range indicatorscale.

26. A grinding machine having in combination with a bed, a reciprocablework supporting table member movable on the bed, driving connections forreciprocating the table member including a slow fast clutch, power meansfor driving the table, manual devices for operating the table, apower-manual clutch for connecting said power drive or manual drivealternatively to the driving connections for the table including saidslowfast clutch, and control devices comprising a power feed selectordevice for determining the position of said slow-fast clutch, a manualfeed selector device for determining the position of said siow fastclutch, and means for controlling the position of said power-manualclutch acting simultaneously to render the corresponding one or saidselector devices operative to determine the position of the slow-fastclutch.

2'7. A grinding machine having in combination with a bed, a reciprocablework supporting table member movable on the bed, driving connections forreciprocating the table member including a slow-fast clutch, power meansfor driving the table, manual devices for operating the table,electrical connections including a power feed selector elementadjustable to shift said clutch alternatively for slow or fast poweroperation of the table, electrical connections including a manual feedselector element adjustable to shift said clutch alternatively for slowor fast, manual operation of the table, and means to connect saiddriving connections for power or manual operation of the table, andsimultaneously to position said slow-fast clutch in accordance with thesetting of the corresponding operative power or manual speed selectorelement.

accuses and said manual driving means alternatively to the table, meansfor reversing the motor at the end oi the table travel in eachdirection, a starting and stopping switch for the motor, electricallyoperated means for controlling the position of said clutch, and amanually operable device ineluding subsidiary switch connections {oroperating said switch to start the motor and simultaneously to move saidclutch to power position, and alternatively to stop the motor andsimultaneously to return said clutch to manual position. a

29. A grinding machine having in combination with a bed, a worksupporting table movable on the bed, driving connections for the tableincluding a reversible electric motor, a manually operable member fordriving the table, a powerrnanual clutch shittable to connect said motorand said manual means alternatively to the table, means for reversingthe motor at the end or the table travel in each direction, a startingand stopping switch for the motor, electrically operated means forcontrolling the position of said clutch, a manually operable controldevice including subsidiary switch connections ior operating said switchto start and stop the motor. subsidiary switch connections renderedoperative upon starting the motor to move said clutch to power position,subsidiary switch connections rendered operative in stopping the motorto return the clutch to manual position, and including means to delaythe operation of said latter subsidiary switch connections to shift thecluwh until1 the motor has reached substantially zero 96 30. In amachine tool, the combination of a base, a movable support, drivingconnections for the support, including a variable speed reversibleelectric motor and a fast-slow clutch for driving the support, andcontrol devices for the support comprising means for adjusting the motorspeed, means for shifting said clutch, a reversing lever, and meanscontrolled by support movement tor reversing the lever, means actuatedby movement or the lever to slow the motor to a predetermined slow speedindependently of said adjustment, motor reversing switches actuated bycontinued movement of the lever, and means controlled by the clutchshifting means to disable said means for slowing the motor when theclutch is shifted to slow position. v

support and on said base to control the move ment or the support, switchconnections con trolled by the actuation of said control element by itsdog to reduce the motor speed, and limit switch connections actuated bycontinued movement of said control element by its dog to arrest supportmovement.

32. In a. machine tool, the combination of a base, a movable support,driving connections for the support including a reversible electricmotor, a reversing switch for the motor, means for varying the motorspeed, and control devices for the support comprising a reversing leverhaving alternative running positions and cooperating reversing dogsrelatively located on the support and on said base to control themovement of the support, switch connections rendered operative bymovement or the reversing lever past a predetermined position to reducethe speed of the motor to a predetermined slow rate, and switchconnections rendered operative by further movement of the reversinglever toward the aitemate running position to reverse the motor at thefaster rate.

33. In a machine tool, the combination 0! a base, a movable support,driving connections for the support including a variable speedreversible electric motor, and control devices for the supportcomprising a reversing lever having alternative running positions andcooperating reversing dogs rendered operative by support movement forshitting the lever from one to the other of said positions to reversethe direction of support of means for reciprocating the table between 45limiting positions at a uniform rate of travel and for stopping and iorstarting the table from said positions, said means including an elementshiftable to bring said table to a quick stop, adjustable ment, and anelectrically controlled mechanism which is actuated in timed relationwith said shiftable element to start the table moving in dogs on saidtable to actuate mid shiftable elea reverse direction after apredetermined time a

